It is known in the art that automotive vehicles are commonly equipped with audio radios that receive and process signals relating to amplitude modulation/frequency modulation (AM/FM) antennas, satellite digital audio radio systems (SDARS) antennas, global positioning system (GPS) antennas, digital audio broadcast (DAB) antennas, dual-band personal communication systems digital/analog mobile phone service (PCS/AMPS) antennas, Remote Keyless Entry (RKE) antennas, Tire Pressure Monitoring System antennas, and other wireless systems.
Currently, patch antennas are typically employed for reception and transmission of GPS [i.e. right-hand-circular-polarization (RHCP) waves] and SDARS [i.e. left-hand-circular-polarization (LHCP) waves]. Patch antennas may be considered to be a ‘single element’ antenna that incorporates performance characteristics of ‘dual element’ antennas that essentially receives terrestrial and satellite signals. SDARS, for example, offer digital radio service covering a large geographic area, such as North America. Satellite-based digital audio radio services generally employ either geo-stationary orbit satellites or highly elliptical orbit satellites that receive uplinked programming, which, in turn, is re-broadcasted directly to digital radios in vehicles on the ground that subscribe to the service. SDARS also use terrestrial repeater networks via ground-based towers using different modulation and transmission techniques in urban areas to supplement the availability of satellite broadcasting service by terrestrially broadcasting the same information. The reception of signals from ground-based broadcast stations is termed as terrestrial coverage. Hence, an SDARS antenna is required to have satellite and terrestrial coverage with reception quality determined by the service providers, and each vehicle subscribing to the digital service generally includes a digital radio having a receiver and one or more antennas for receiving the digital broadcast. GPS antennas, on the other hand, have a broad hemispherical coverage with a maximum antenna gain at the zenith (i.e. hemispherical coverage includes signals from 0° elevation at the earth's surface to signals from 90° elevation up at the sky). Emergency systems that utilize GPS, such as OnStar™, tend to have more stringent antenna specifications. Unlike GPS antennas, which track multiple satellites at a given time, SDARS patch antennas are operated at higher frequency bands and presently track only two satellites at a time.
Although other types of antennas for GPS and SDARS are available, patch antennas are preferred for GPS and SDARS applications because of their ease to receive circular polarization without additional electronics. Even further, patch antennas are a cost-effective implementation for a variety of platforms. However, because GPS antennas receive narrowband RHCP waves, whereas, SDARS antennas receive LHCP waves with a broader frequency bandwidth, both applications are independent from each other, which has resulted in an implementation configuration utilizing a first patch antenna for receiving GPS signals and a second patch antenna for receiving SDARS signals.
Because multiple patch antennas are implemented for receiving at least a first and second band of signals, additional materials are required to build each patch antenna to receive each signal band. Additionally, the surface area and/or material of a single or multiple plastic housings that protects each patch antenna is increased due to the implementation of multiple patch antenna units, which, if mounted exterior to a vehicle on a roof, results in a more noticeable structure, and a less aesthetically-pleasing appearance.
Thus, cost and design complexity is increased when multiple patch antennas are implemented for reception of at least a first and second band of signals, such as, for example, GPS and SDARS signals. As such, a need exists for an improved antenna structure that reduces cost, materials, and design complexity.